Physical vapor deposition method using backside gas cooling of workpieces

ABSTRACT

A circular PVD chamber has a plurality of sputtering targets mounted on a top wall of the chamber. A pallet in the chamber is coupled to a motor for rotating the pallet about its center axis. The pallet has a diameter less than the diameter of the circular chamber. The pallet is also shiftable in an XY direction to move the center of the pallet beneath any of the targets so all areas of a workpiece supported by the pallet can be positioned directly below any one of the targets. A scanning magnet is in back of each target and is moved, via a programmed controller, to only be above portions of the workpiece so that no sputtered material is wasted. For depositing a material onto small workpieces, a cooling backside gas volume is created between the pallet and the underside of sticky tape supporting the workpieces.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.14/923,357, filed on Oct. 26, 2015, assigned to the present assignee.

FIELD OF THE INVENTION

This invention relates to sputtering systems and, in particular, tomethods for controlling the sputtering of materials on the workpieces.

BACKGROUND

Sputtering systems are widely used for depositing materials onworkpieces, such as semiconductor wafers, display panels, mechanicalparts, etc. Sputtering is sometimes referred to as physical vapordeposition, or PVD. In a sputtering operation, thin films comprisingmaterials such as Al, Au, Cu, and Ta are deposited in a vacuum on theworkpieces. It is common to deposit a stack of thin films of differentmaterials, such as to form a tri-layer structure comprising Ti/Cu/Au.

Applicant had previously developed a PVD system having multiplewedge-shaped targets around a top wall of a circular vacuum chamber,where workpieces are mounted on a rotating circular pallet below thetargets for being positioned under the different targets. The diameterof the pallet was approximately the same as the inner diameter of thevacuum chamber. The rotating pallet not only creates a more uniformdeposition, but allows each workpiece to be positioned under targets ofdifferent materials for depositing a stack of different materials on theworkpieces. This is described in Applicant's U.S. Pat. No. 7,682,495.However, with such a system, the center of the pallet could not bepositioned under any of the targets. This was acceptable when theworkpieces, such as silicon wafers, were mounted on the pallet away fromthe center so as to be fully under a target for sputtering. If theworkpiece was a single large rectangular panel that overlaid the centerof the rotating pallet, the center portion of the panel could not bepositioned under a target by the rotating pallet, resulting in thenon-coverage of the middle area by the targets.

Thus, what is needed is a technique for performing a PVD process on alarge panel on a rotating pallet in a PVD chamber with multiple targets.

Further, for a large rectangular workpiece on the circular pallet, aportion of the targets must be directly above the corners of therotating workpiece (where the corners extend near the outer perimeter ofthe pallet) for sputtering on the corner areas, but the sputteringmaterial is wasted when the workpiece is not directly below the entiretarget, such as when a flat side of the rectangular workpiece (closer tothe center of the pallet) is under only a portion of the target. Also,if multiple wafers are mounted on the pallet with spaces between them,sputtered material is wasted if it lands between the wafers.

Thus, what is also needed is a technique for performing a PVD process ona large panel (or other workpieces) on a rotating pallet in a PVDchamber where sputtering is only from portions of the targets that aredirectly above the workpiece.

The metal pallet is cooled using a liquid coolant flowing in the pallet.The pallet then cools flat wafers that are directly in contact with thepallet surface. However, for some uses, the workpiece is not in directcontact with the pallet surface and cannot be cooled by the pallet. Suchis the case where the PVD system is used for depositing a metal layerover an array of IC packages for EMI shielding or for other applicationswhere the workpiece is not in direct contact with the cooled pallet.

Thus, what is also needed is a technique for cooling workpiecessupported by the pallet but are not in direct thermal contact with thepallet.

Other improvements are also described.

SUMMARY

Some examples of uses of the present invention are described below.

In one embodiment, a circular rotating pallet is provided in a circularPVD chamber. The pallet has a diameter significantly smaller than thediameter of the chamber. Multiple wedge-shaped targets are arranged in acircle at the top of the chamber. No target is over the center of thechamber. If a large panel, such as a panel covering a majority of therotatable pallet, is to be subject to a PVD process, an XY stage shiftsthe rotatable pallet in any XY direction to cause the middle area of thepallet (and panel) to be directly under any sputtering target so thatthe entire panel can receive the sputtered material by a combination ofthe rotation of the pallet and the XY shifting of the pallet. A similarbenefit is obtained when any workpiece is positioned near the center oredge of the pallet.

In the event that the panel is rectangular, its corners will extendcloser to the walls of the chamber than the sides of the panel. Thetargets must extend close to the walls of the chamber to overlie thecorners of the panel while the sputtering is occurring and when therotating pallet positions a corner below a target. However, sputteringfrom the outer edge areas of the target when only the side of the panelis below the target wastes sputtering material. To control the area ofsputtering from the target, a magnet behind each target shapes theplasma. The magnet scans in an arc from side to side and also movesalong the long axis of the target. The magnet can be controlled to coverthe entire back area of the target or any portion of it. Therefore, themagnet is controlled to cover only the areas of the target that aredirectly above a surface of the workpiece (e.g., the panel). This avoidswasting sputtered material, creates a more uniform deposition, andimproves efficiency.

Such a benefit is also realized when there are spaces between workpieceson the pallet, and the sputtered material between the workpieces is tobe minimized.

If the workpiece is secured to the pallet so that there is good thermalcontact, the workpiece is cooled by cooling the pallet with an internalcoolant flow. However, in the situation where an array of packaged diesis supported on a sticky tape and the PVD system is to cover thepackages with a metal film for shielding, the packaged dies are not ingood thermal contact with the pallet and need to be cooled during thePVD process. For example, the packages may only be rated to withstand150° C. and the PVD process would raise the temperature to 220° C.without some sort of cooling.

In one embodiment, the packages are mounted on a sticky tape havingrectangular holes so that a portion of the bottom surfaces of thepackages is exposed through the holes, and the edges of the packages arestuck to the top surface of the tape. The land grid array (LGA) or ballgrid array (BGA) portions of the packages extend through the holes inthe tape. The thin sticky tape is supported by a high magneticpermeability metal frame, such as a steel frame. If the metal frame iscircular, the metal frame and tape supporting the packages are mountedover a circular ridge on the pallet that only contacts the outerperiphery of the tape. Magnets on the pallet then draw the metal frametoward the pallet, and the ridge creates a good gas seal between thetape and the ridge to form a backside gas volume behind the tape. Holesin the pallet then allow a cooling backside gas to cool the back of thetape and the packages. In one embodiment, the temperature of thepackages is limited to 110° C. due to the backside gas, while thetemperature would be 220° C. without the backside gas.

The backside gas cooling technique may also be used for any wafer thatis not in direct thermal contact with the cooled pallet, such as anywafer mounted on a sticky tape when supported by the pallet.

The backside gas may even cool the workpiece to below the temperature ofthe pallet. This is useful to control stress and grain structure.

The above descriptions are only specific examples of the use of thetechnology, and many other benefits can be achieved by the inventive PVDsystem depending on the specific application of the PVD system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the sputtering system in accordance with oneembodiment of the invention.

FIG. 2 is a bisected perspective view of the system of FIG. 1.

FIG. 3 is a bisected side view of the system of FIG. 1.

FIG. 4 is a perspective view of an XY stage which moves the rotatingpallet in a controlled XY direction.

FIG. 5 is a schematic cross-sectional view of the pallet, showing theliquid coolant channel, the backside coolant gas channel, the palletmotor, the XY mount for the motor and pallet, the RF/biasing source, andthe programmed controller (a processor).

FIG. 6 is a top down view of the magnetron over the wedge-shaped targetsabove the vacuum chamber.

FIG. 7 illustrates how the magnet over the target moves linearly as wellas in an arcing motion to cover all areas of the target and to preventsputtering over areas where no workpiece is directly underneath thetarget.

FIG. 8 illustrates how the magnet is composed of many smaller magnets tocreate a substantially uniform magnetic field behind the target.

FIG. 9 illustrates how a large rectangular panel (a workpiece on thepallet in the vacuum chamber) is rotated by the pallet and shifted in anXY plane below the targets and how the magnets for the targets can becontrolled to only pass over portions of the target directly above thepanel.

FIG. 10 illustrates how the rectangular panel is rotated and shifted inan XY plane within the vacuum chamber to obtain full sputtering coverageof the panel.

FIG. 11 illustrates the pallet on which is mounted four steel ringssupporting a sticky tape, with packaged integrated circuit chips mountedon the tape for receiving a sputtered metal shielding layer.

FIG. 12 is a schematic cross-section of one of the steel rings beingmounted over the pallet, showing a backside cooling gas channel in thepallet, a circular ridge, and magnets on the pallet.

FIG. 13 illustrates how the magnets on the pallet pull down the steelring to create a backside gas seal around the periphery of the stickytape for cooling the packages with a backside gas.

Elements with the same numbers in the various figures are the same.

DETAILED DESCRIPTION

The present assignee has obtained a U.S. Pat. No. 7,479,210, and has apublished application US 2012/0024694, describing a sputtering tool, andthe present invention is an improvement over those tools. U.S. Pat. No.7,479,210 and US 2012/0024694 are incorporated herein by reference.Accordingly, only aspects of the improved tool that are relevant to thepresent invention are described herein in detail. Other features of thetool may be obtained by reviewing the assignee's above-identifiedpublications.

FIGS. 1-3 illustrate the inventive sputtering system 12 in accordancewith one embodiment of the invention. The sputtering system 12 may beused for workpieces such as semiconductor wafers, display panels,mechanical parts, and other workpieces requiring the deposition of thinfilms. Examples of thin films include Al, Cu, Ta, Au, Ti, Ag, Sn, NiV,Cr, TaNx, Hf, Zr, W, TiW, TiNx, AlNx, AlOx, HfOx, ZrOx, TiOx, magneticfilms, and various alloys of these materials.

In FIG. 1, the top cover 14 covers the magnetron and other componentsabove the vacuum chamber 16. A rotating pallet and various targetsreside within the vacuum chamber 16.

In one embodiment, the system 12 can process any size workpiece that canfit on the rotating pallet 18 (FIGS. 2 and 3), such as a large displaypanel. Alternatively, the system 12 can simultaneously process multiplestandard semiconductor wafers (e.g., five or more) using multiplesputtering targets (e.g., 3-6).

The pallet 18 rotates to move a workpiece directly below an appropriatewedge-shaped target. Each target may be a different material for formingsuccessive thin films of different materials on a workpiece, or thetargets may be the same material. The targets are directly below anassociated target backing plate 20 (FIG. 2).

The pallet 18 has a central shaft 22 (FIG. 3) that is rotated by a motor24, such as a stepper motor or a servo motor. The pallet 18 may beformed of aluminum. The pallet 18 may be continuously rotated at anyspeed or may be temporarily stopped to control the deposition of asputtered material from a target overlying a workpiece.

The servo or stepper motor 24 is mounted on a mounting area 26 of an XYstage 28. FIG. 4 illustrates the XY stage 28 in greater detail. The XYstage 28 has a stationary top plate 30 mounted to the bottom surface ofthe vacuum chamber 16. A middle plate 32 moves in an X directionrelative to the top plate 30 using an X linear motor 34. The linearmotor includes a small rotating motor with a cam that engages a longscrew so that the screw is moved in a linear direction with respect tothe motor. The motor may be attached to the top plate 30, and the screwis rotatably mounted on the middle plate 32. Tracks keep the middleplate 32 slidably attached to the top plate 30. Similarly, the bottomplate 36 is slidably attached to the middle plate 32 using tracks and aY linear motor 38 that is identical to the X linear motor 34.

A large center opening 42 in the XY stage 28 accommodates the palletshaft 22 and allows some XY movement of the shaft 22 within the opening42. As shown by the arrows 44 in FIG. 3, the XY stage 28 can move therotatable pallet 18 within the vacuum chamber 16 in an XY plane. Theamount of movement can be any amount, depending on the size of thesystem. In one embodiment, the movement may be greater than 4 inches.

A bellows 46 (FIG. 3) extends through the hole 42 in the XY stage 28 andsurrounds the shaft 22 to maintain a vacuum seal around the shaft 22.

The magnetron assembly 50 in the top (non-vacuum) compartment of thesystem 12 moves a magnet around each of the target backing plates 20.The magnets attract the ions in the sputtering gas to the targets toaccelerate and direct the ions. The ions then knock out atoms of thetarget for sputtering the target material on the workpiece substantiallydirectly below the magnet. The aluminum pallet 18 has a potential thatattracts the sputtered material to the workpiece. More detail regardingthe magnetron assembly 50 is presented later.

FIG. 5 is a schematic cross-sectional view of an area of the pallet 18,with various features exaggerated for ease of illustration. The palletmotor 24 is shown rotating the shaft 22, and the motor 24 is mounted onthe XY stage mounting area 26.

The pallet 18 has liquid channels or tubing 51 that receive a liquidcoolant from a recirculating cooling source 52. The coolant flowsthrough input and output lines 54/55 in the shaft 22 and within thepallet 18. A coupler 58 provides a rotating seal for the input/outputlines 54/55.

The coupler 58 is shown also coupling an optional RF source 60 to thealuminum pallet 18 for generating a plasma and for attracting ions tothe workpiece.

In addition to cooling the pallet 18, a backside coolant gas source 62is also provided to supply a backside gas, such as argon or other inertgas, through openings 64 in the pallet 18. A gas channel 66 in the shaft22 supplies the gas to a diffuser 68 in the pallet 18 for distributingthe gas to the openings 64. The coupler 58 may also provide a gas sealto allow the shaft 22 to rotate while the backside gas is beingsupplied. A gas exit channel for maintaining a desired gas pressure isoutside of the cross-section. Optionally, the gas may also exit into thechamber without a return path. The use of the backside gas to cool aworkpiece is discussed later. The backside gas feature is not alwaysused.

A controller 70 comprises a programmed processing system andautomatically controls the XY stage 28, motor 24, RF source 60,coolants, and target magnets pursuant to a pre-programmed routine todeposit one or more sputtered layers on the workpiece.

The RF source 60 (FIG. 5) is electrically coupled to the aluminum pallet18 by the rotatable coupling 58 to create a plasma. In anotherembodiment, the pallet 18 is grounded, floated, or biased with only a DCvoltage source.

When the chamber 16 is evacuated and filled with a certain amount of Argas at a certain pressure (for example, 20 milli-torr) and the gas isenergized with a DC source, an RF source, or a combination of the twosources, an electromagnetic field is coupled inside the chamber toexcite a sustained high density plasma near the target surface. Theplasma confined near the target surface contains positive ions (such asAr+) and free electrons. The ions in the plasma strike the targetsurface and sputter material off the target. The workpieces receive thesputtered material to form a deposited layer on the surface of theworkpieces. In one instance, up to twenty kilowatts of DC power can beprovided on each target. In such a case, each target can depositapproximately 1 micron of metal per minute on an underlying work piece.A typical RPM of the pallet 18 during the deposition process is 5-30RPM. The pallet 18 may be rotating during deposition or stopped.

The chamber wall is typically electrically grounded during sputteringoperations.

A bias voltage on the workpieces can drive a flux of an electricallycharged species (Ar+ and/or atomic vapor sputtered off the target) tothe workpieces. The flux can modify the properties (for example,density) of the sputtered material to the wafers.

Generating a plasma for sputtering and the various biasing schemes arewell known, and any of the known techniques may be implemented with thedescribed sputtering system.

FIG. 6 is a top down schematic illustration of the target backing plates20 and the magnetron assembly 50. Targets are mounted to the top ceilingof the vacuum chamber directly under the target backing plates 20. Thetargets have the same outline as the plates 20. A contamination shield71 (a vertical wall) extends any length between targets for preventingcross-contamination. Some possible positions for the magnet 72 duringmotion are shown in dashed outline.

FIG. 7 illustrates a single scanning magnet 72 over a target 74. Theview is looking up from the target 74 though the target backing plate.In one embodiment, the delta-shaped magnet 72 is about 10.7 inches (27cm) long and about 3 inches (7.6 cm) wide at its widest part. A motor 76(also shown in FIG. 3) moves all magnets 72 back and forth in an arcpath 78 over the target backing plate 20 and target 74. The motor 76 maybe any type of scanning actuator, such as a servo/stepper. The rate ofscan can be any rate. The motor 76 scans the magnet 72 to the left andright edges of the target for each scan of the magnet 72. When themagnet 72 is over a portion of the target 74, that portion will beprimarily bombarded by ions in the plasma and deposit sputtered materialon the underlying workpiece. The magnet 72 is also moved linearly alongany portion of the length of the target 74 by a linear motor. The linearmotor includes a motor 80 that rotates a screw 82 within a track 84. Theback of the magnet 72 has a threaded coupling (like a nut) that is movedlinearly by the rotating screw 82 in the direction of the arrow 86. Thelinear motor can be any type of linear actuator.

A scanning controller 88 controls the simultaneous arcing scan of themagnets 72, and a linear movement controller 90 independently, andindividually, controls the linear movement of an associated magnet 72.Each magnet, associated with a different target, may be controlleddifferently, depending on the requirements of the sputtering for thattarget. The controllers 88 and 90 may be part of the controller 70 ofFIG. 5.

More specifically, the function of the magnet 72 is as follows. Themagnet 72 confines the plasma to the target area. The resulting magneticfield forms a closed-loop annular path acting as an electron trap thatreshapes the trajectories of the secondary electrons ejected from targetinto a cycloidal path, greatly increasing the probability of ionizationof the sputtering gas within the confinement zone. Inert gases,specifically argon, are usually employed as the sputtering gas becausethey tend not to react with the target material or combine with anyprocess gases and because they produce higher sputtering and depositionrates due to their high molecular weight. Positively charged argon ionsfrom the plasma are accelerated toward the negatively biased target andimpact the target, resulting in material being sputtered from the targetsurface.

The scanning controller 88 oscillates all the magnets 72 back and forthin unison over their associated targets at an oscillating period ofbetween 0.5-10 seconds. The magnets 72 are oscillated so that themagnetic fields are not always at the same position relative to thetarget. By distributing the magnetic fields evenly over the target,target erosion is uniform.

FIG. 8 illustrates the magnet 72 in more detail. The magnet 72 has atriangular or delta shape with rounded corners. In one embodiment, thethickness of magnet 72 is between 0.5-1¼ inch thick (12-31 mm). In theexample of FIG. 8, there are three rings (nested patterns) of individualmagnets 94, where adjacent rings have opposite poles so that a magneticfield spans across one ring to the next. Some magnetic field lines 96are shown. Since there are three rings of magnets, there are tworacetracks of field lines. These magnetic fields pass through the targetbacking plate 20 (FIG. 6) and intersect the target attached to theunderside of the target backing plate 20. The plasma density at thetarget (and thus the erosion rate) is greatest at the highest magneticfield intensity. The sizes, shapes, and distribution of the individualmagnets 94 are selected to create a uniform erosion of the target. Themagnets 94 are mounted to a magnetic backing plate 98, also known as ashunt plate, which may be formed of a ferrous material. The shape andmagnetic properties of the shunt plate 98 may be altered to optimize theperformance of the magnet 72. The magnet 72 may instead be anelectromagnet.

FIG. 9 is identical to FIG. 6 except that the outline of a relativelarge panel 100 (a workpiece) is shown mounted on the rotating pallet.

FIG. 10 shows the panel 100 mounted on the pallet 18. The inside wall102 of the vacuum chamber 16 is also shown. Note that the diameter ofthe pallet 18 is significantly smaller than the diameter of the chamber16 to allow the pallet 18 to be moved in an XY plane within the chamber16.

In the prior art sputtering chambers having a rotating pallet, if alarge workpiece, such as the panel 100, were mounted on the pallet, themiddle area of the workpiece could not be positioned under a target,since the targets do not extend over the center of the chamber. However,in the present invention, the center 104 of the pallet 18 is movable soas to be under any of the targets by shifting the XY stage 28 (FIGS. 3and 4). Therefore, by controlling the rotation of the pallet 18 inconjunction with the XY stage 28, all portions of the panel 100 may bepositioned under any target for receiving a sputtered layer of thetarget material. The arrows 106 and 108 illustrate the rotation of thepallet 18 and the XY movement of the pallet 18. In one embodiment, thediameter of the pallet 18 is at least 4 inches less than the diameter ofthe chamber 16 to allow the center of the pallet 18 to be shifted up toplus/minus 2 inches in order to position the panel 100 under a target.

Referring back to FIG. 9, it can be seen that the corners of therectangular panel 100 extend closer to the wall 102 of the chamber 16than the flat sides of the panel 100. When the corner of the panel 100is below the outer end of the target (having the same outline as thetarget backing plate 20), the magnet 72 needs to be positioned, via thescanning and linear motors 76/80, above the outer end of the target topromote sputtering onto the corner area of the panel 100. However, whenthe side of the panel 100 is below a target, the side may only be belowthe inner one-third or less of the target. Thus, sputtering from theouter end of the target will waste target material (and generate debris)when no portion of the panel 100 is below the outer edge. Therefore, inaccordance with one embodiment of the invention, the linear movementcontroller 90 (FIG. 3) is programmed to control the magnet 72 movementso that the magnet 72 is substantially moved only over portions of thepanel 100 (or other workpiece). The dimensions of the panel 100 areprogrammed into the controller 70 (FIG. 5) or 90 (FIG. 7) and theposition of the panel 100 at any time is determined by the position ofthe pallet 18.

In one application, the magnet 72 is continuously scanned in an arc viathe motor 76 and controller 88 (FIG. 7) during the entire sputteringprocess. In another application, the controllers 88/90 of FIG. 7 areprogrammed to control the magnet 72 to stop scanning or slow scanning,via the combination of the scanning/linear motors 76/80, in order tominimize the waste of target material by reducing/preventing sputteringwhen there is no workpiece under areas of the target.

If all the targets are the same material and the pallet is rotating therectangular panel 109 under the targets, the scanning/linear motors forone magnet will control their associated magnet in one way to ensure themagnet is only over a portion of the panel 100 and the scanning/linearmotors for another magnet may control their associate magnet in adifferent way to ensure all magnets are only above a portion of thepanel 100 so no sputtering material is wasted.

Although the panel 100 in FIG. 9 is shown having a diagonal dimensionapproximately equal to the diameter of the pallet 18, the panel 100 canbe any size. If the workpiece is small, such as a silicon wafer, thewafers may be positioned around the periphery of the pallet 18 so XYshifting of the pallet 18 is not needed to position the wafers directlyunder each target.

The XY shifting of the pallet 18 and the control of the magnets 72 tolimit the waste of target material are also applicable where multiplewafers are distributed over the pallet 18, where there are spacesbetween the wafers, and where the wafers cover the center area of thepallet 18. The positioning of the magnets 72 and the shifting of thepallet 18 are controlled to substantially limit sputtering material toonly the wafer surfaces and not the pallet 18 surface.

Another use of the sputtering system 12 is to sputter a copper film orother metal film over a batch of packaged integrated circuit chips, orover some other structures, to act as a shield to mitigateelectromagnetic interference (EMI). Such packaged ICs would not havegood thermal contact to the pallet 18 so could not be cooled by coolingthe pallet 18 (using the liquid coolant). One technique to support anarray of packaged ICs is shown in FIGS. 11-13.

In FIG. 11, steel rings 112, or other rings formed of a high magneticpermeability material, have a sticky tape 114 secured to their undersideso the tape 114 is taut across the opening of the rings 112. The rings112, acting as frames, may be other shapes, such as rectangular. Thetape 114 has rectangular openings 116 (FIG. 12) that are customized forthe particular packages 115 being shielded. The openings 116 are justlarge enough for the bottom land grid array (LGA) or ball grid array(BGA) electrodes 118 to be within the openings, and the outer edges ofthe package create a seal with the top surface of the sticky tape 114,as shown in FIG. 12. It is not desirable to directly adhere theelectrodes 118 to the sticky tape for at least the reasons that thesputtered material for the shielding layer may short out the electrodesand that the metal electrodes may be pulled off the packages when theyare removed from the tape 114.

In the example shown, there are four identical arrays of packages 115mounted on the pallet 18 for receiving a metal shielding layer.

In one example, if the packages 115 were not cooled somehow during thesputtering process, the temperature of the packages 115 would reach 220°C., and the packages 115 are only rated to withstand 150° C. Therefore,so means of cooling the packages 115 is required.

Applicant's system cools the packages 115 with a recirculating backsidegas, such as argon or other inert gas. As shown in FIG. 5, the shaft 22of the pallet 18 has a channel 66 for a coolant gas, and the pallet 18has a manifold 68 and openings 64 for the gas to exit the surface of thepallet 18. As shown in FIG. 12, the pallet 18 also includes openings 119for a return path of the gas for cooling the gas. The gas exit channelis also along the pallet shaft.

In FIG. 12, the pallet 18 surface includes magnets 120 and a circularridge 122, assuming the opening of the rings 112 is circular. Othershapes are envisioned.

As shown in FIG. 13, the magnets 120 pull the steel ring 112 downward sothat the ridge 122 creates a gas seal with respect to the underside(non-sticky side) of the tape 114 and creates an open backside gasvolume. The magnets 120 do not need to contact the entire periphery ofthe ring 112. The magnets 120 may be permanent magnets orelectromagnets.

In one embodiment, the pallet 18 has many functions, and a specialsurface plate 126 (FIG. 12), having the magnets 120 and ridges 122, isaffixed to the top of a flat pallet plate 128, such as with screws. Forother uses, a different surface plate may be affixed to the flat palletplate 128 such as for sputtering on the panel 100 in FIG. 10 or onmultiple wafers.

During sputtering of Cu to deposit a shielding layer over the packages115, the backside gas 129 is recirculated, by the backside coolant gassource 52, within the backside gas volume 130 behind the packages 115 toa predetermined pressure. The heat is removed from the packages 115 andthe tape 114 by the recirculating backside gas 129. The temperature ofthe packages 115 is highly controllable by controlling the flow of thebackside gas. Return paths 119 for the gas 129 may be included aroundthe periphery of the backside gas volume 130.

Other workpieces besides packages may be cooled using the basictechnique of FIGS. 11-13. High heat dissipation during sputtering isessential for devices such as microprocessors, analog chips, etc. Thesewafers may be very thin (e.g., 30-200 microns) as a result of aback-grinding process, where the front surface of the wafer is mountedon a sticky tape during the grinding process. The tape 114 is thenmounted to the rings 112, and a backside metal (e.g., Ti/Ni/Au) issputtered over the back surface of the wafers. The wafers are cooled bythe backside gas. The wafers may then be singulated while still attachedto the sticky tape 114. The invention applies to any workpiece that maynot be in good thermal contact with the pallet 18 or needs extracooling.

The invention pertaining to FIGS. 11-13 is independent of the rotatingpallet 18 and the other aspects of the PVD system described with respectto FIGS. 1-10. The support surface for the steel rings 112 may bestationary. The sticky tape 114 can be used in other ways, such assupporting workpieces without openings in the tape 114. The inventionwill cool the backside of the tape and any workpieces in thermal contactwith the tape 114. In one embodiment, the ring 112 material itself maynot have a high magnetic permeability, such as the ring 112 being adielectric, but the ring 112 has areas of high magnetic permeability,such as thin steel plates adhesively affixed to the bottom of the ring112.

Conventional aspects of the system that have not been described indetail would be well known to those skilled in the art. U.S. Pat. No.6,630,201 and U.S. Patent Application Publication 2002/0160125 A1 areincorporated herein by reference for certain conventional aspectsprimarily related to creating a plasma and supplying gas to a processchamber.

Although the system has been described with respect to examples offorming a metal film on workpieces, the system may deposit any material,including dielectrics, and may process any workpiece. In one embodiment,the system is used to deposit materials on multiple thin film transistorarrays for LCD panels. The invention is not limited to the specificexamples described herein.

Having described the invention in detail, those skilled in the art willappreciate that, given the present disclosure, modifications may be madeto the invention without departing from the spirit and inventiveconcepts described herein. Therefore, it is not intended that the scopeof the invention be limited to the specific embodiments illustrated anddescribed.

What is claimed is:
 1. A method of operation of a physical vapordeposition device, the device having a chamber configured to create alow pressure environment in the chamber while sputtering materials on aworkpiece, the method comprising: providing a workpiece support platformin the chamber, the platform having openings for a backside gas;mounting a workpiece on a sticky tape, wherein a ring provides a framefor the sticky tape; providing one or more magnets on the supportplatform for attracting the ring to the one or more magnets; positioningthe ring over the one or more magnets such that the ring is attracted tothe one or more magnets; providing a ridge on the support platform thatcreates a gas seal with respect to the sticky tape as the ring isattracted to the one or more magnets on the support platform, so that anarea between the tape and the support platform forms a sealed backsidegas volume; and introducing a backside gas into the backside gas volumefor cooling the workpiece supported by the tape.
 2. The method of claim1 wherein the sticky tape has at least one opening that exposes a backsurface of the workpiece to the backside gas volume.
 3. The method ofclaim 1 wherein the workpiece is one of a plurality of workpiecessupported on a top surface of the sticky tape for batch processing ofthe workpieces.
 4. The method of claim 1 wherein the one or more magnetsare permanent magnets.
 5. The method of claim 1 wherein the ring isformed of a high magnetic permeability material.
 6. The method of claim1 wherein the ring is formed of steel.
 7. The method of claim 1 furthercomprising depositing a metal shield over the workpiece.
 8. The methodof claim 1 further comprising depositing a backside metal over theworkpiece.